| Abstract | Webs are a major element in the energy economy of spiders. The sticky silk of orb web capture spirals is costly to produce and is a limiting factor in web building (Venner et. al., 2001). Consequently, spiders in poor condition may be forced to modify aspects of their web geometry (Blackledge et. al. 2002). In this study, we are examining whether individual garden spiders (Argiope sp.) modify their webs as a consequence of the bioaccumulation of toxic heavy metals. We report here on the perfection of digital orb web photography and the interactive generation of web measurements from digital images using software. Film-based orb web photography has involved coating the web surface with a reflective powder (e.g. cornstarch) and illumination of this surface with a flash unit casting light parallel to the web plane. Using orb webs of several species, we found that this approach works well for digitally-based orb web photography, especially if a black background isprovided and both camera and web are shaded with an umbrella. To calibrate subsequent measurements, an object of known size (fiducial) was placed in or on each web prior to photography. For image analysis, we created command codes in the MATLAB development environment to interactively generate the following web parameters: surface area; number of radii; number of spirals; inter-spiral distances; and inter-radii angles. We are have collected web images from spiders whose heavy metal contents will also be determined, enabling us to detect significant relationships between metal concentrations and any web parameter metric(s). |
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